The present invention is directed to liquid circulation cooling systems for electronic devices and the like, and more particularly to apparatus for detecting, locating and isolating coolant leaks at the pipe joints of such systems.
Liquid cooling is finding increased application in the electronics industry due to the limited heat dissipation capability of forced air cooling systems and the desire to minimize cooling system noise levels. FIG. 1 depicts a liquid cooling system 10 for one or more heat producing electronic devices 12. The device 12 is typically mounted on a circuit board 14, and its upper surface is secured to a cold plate 16 of cooling system 10 by thermal paste, thermal interface material or other means so that heat generated by the device 12 is conducted to the cold plate 16. The cold plate 16 is provided with inlet and outlet pipes 16a, 16b through which a liquid coolant such as water or a water-glycol solution is circulated. The coolant is stored in a tank or reservoir 18, and a pump 20 draws coolant out of tank 18 for delivery to the cold plate inlet pipe 16a. Heated fluid exiting cold plate 16 through outlet pipe 16b is supplied to a heat exchanger 22 before being returned to the tank 18. A cooling fan 24 driven by electric motor 26 forces ambient air through the heat exchanger 22, so that the heat transferred from device 12 to the fluid in cold plate 16 is subsequently transferred from the fluid in heat exchanger 22 to circumambient air.
The potential for fluid leaks is a significant concern, particularly in electronic systems where the leaked fluid can damage various electronic devices and potentially create a risk of electrocution or fire. As in any liquid (single phase or multi-phase fluid) circulation system, the most likely sources of leakage in the system 10 are the pipe joints. In the system of FIG. 1, for example, the inlet 16a, 18a, 20a, 22a of each device 16, 18, 20, 22 is coupled to the outlet 16b, 18b, 20b, 22b of another device by a connecting pipe 28, 30, 32, 34, and there is a pipe joint at each such coupling. In the system of FIG. 1, the connecting pipes 28, 30, 32, 34 have an inside diameter that matches the outside diameter of the inlet or outlet pipe to which it is coupled, and a clamp 36 prevents the pipes from becoming uncoupled. Other possible coupling configurations are depicted in FIGS. 2-4, described herein. Although the coupled pipes can be soldered or otherwise sealed to prevent fluid leakage, the possibility of fluid leakage remains due to sealing defects or imperfections that occur over time.
Various systems have been devised to address the aforementioned leakage concerns, most of which include one or more leak detection devices and an alarm or other warning device to alert an operator upon detection of leakage. The detection device typically takes the form of a pair of electrodes separated by an absorbent material that is insulative in the absence of fluid but which dissolves or becomes conductive in the presence of fluid. A circuit responsive to the resistance between the electrodes activates the alarm when a change in resistance indicative of fluid leakage is detected. See, for example, the U.S. Pat. Nos. 4,922,232; 4,974,739; 5,172,730; 5,176,025; and 5,918,267 which pertain to leak detection in pipelines, and the U.S. Pat. Nos. 4,870,477 and 5,086,829, which pertain to leak detection for liquid circulation cooling systems.
The present invention is directed to an improved leak detection apparatus that is particularly suited to liquid circulation cooling systems having pipe joints, including detection devices that envelope the various pipe joints of the cooling system. According to a first embodiment, the detection devices comprise a pair of conductors separated by a wicking material impregnated with a crystalline salt that provides a low resistance electrical path between the conductors in the presence of a leak. According to a second embodiment, the detection devices comprise a pair of dissimilar metal mesh electrodes separated by an electrolyte-impregnated wicking material to form a water-activated battery that energizes an alarm in the presence of a leak. Both embodiments optionally are encased with a water-activated sealing material that hardens in the presence of a leak to contain the leakage.